1. Field of the Invention
This invention relates to a two-part or multipart plastic closure for fastening to the neck of a flexible bottle for dispensing thixotropic fluids.
2. Discussion of Related Art
Thixotropic fluids are fluids with a non-Newtonian flow behavior. A typical example of such a fluid is ketchup. Various liquid soaps also exhibit thixotropic behavior, as do many dispersions. Today, such fluids are sold in flexible plastic containers having closures equipped with a so-called closure membrane. There are many known embodiments of closures equipped with a so-called closure membrane. Examples include those taught by European Patent References EP-A-545 678 and EP-A-442 379, U.S. Pat. No. 2,175,052, or PCT International Application WO-A-2006/119315. The significant advantage of closures having a closure membrane is that the already open container can be stood on its head without the fluid leaking out of it. Pressure exerted on the flexible bottle deforms the closure membrane, the usually slit-shaped opening spreads open, and the fluid can be squeezed out of the bottle. In this case, one problem arises because as the more tautly the membrane is held, the better the closing force is and the quicker the closure closes when the pressure on the container is released. As a result, an ever more powerful vacuum builds up in the container over time so that the bottle becomes more and more deformed as its contents are consumed and also the pressure required to dispense the fluid must be increased. If the closure membrane is stretched less tautly, then at least sometimes, a certain amount of the displaced air can flow back into the container; as a result of this, the closure also tends to drip. Furthermore, the more tautly the closure membrane is stretched, the more the closure tends to open explosively when pressure is exerted, causing a jet to emerge at high velocity and the container to have a tendency to spray.
In order to reduce this problem, a variety of complex closure membrane closures are marketed for which the design of the closure membrane has become more and more complex and the very small component requires more and more effort with regard to its installation in the closure. With these complex closure membranes, it is possible to produce a closing action and an opening of the slit-shaped closure as soon as a pressure difference exists between the atmosphere and the internal pressure of the bottle, which assures the venting of plastic bottles. But merely due to the variety of materials that must be used in these plastic bottles with closure membranes, namely the membrane must usually be made of a silicone rubber and the actual closure also must be produced from a polypropylene because it is not possible to produce them in one injection procedure in the same machine. Also, the silicone rubber part is a relatively expensive part and for this reason alone, it is desirable for it to be as small as possible. When this part is small, however, and is at the same time highly flexible, its installation by machine is extremely complex and malfunction-prone.
Development of the closure according to this invention provides a closure that is limited to the use of thixotropic fluids. Thixotropy is understood to be the property of a non-Newtonian fluid in which the viscosity decreases in response to constant shear stress over a certain period of time. After the shear stress stops, the initial viscosity is reestablished. In other words, the longer a thixotropic fluid is moved, the lower its viscosity becomes. It is normally true that the faster the movement is carried out, the faster the viscosity decreases. In other words, in such a closure, the flow-through direction is changed and the flow is accelerated, thus achieving a good flow capacity of the thixotropic fluid while at the same time, a simple shut-off in the flow direction can prevent leakage at a lower viscosity.
German Patent Reference DE-U-20112974 discloses a plastic closure in which an inner cap with two concentric walls can be inserted underneath the pouring spout and in the assembled state, the pouring spout protrudes into the region of the inner concentric wall. This produces an outflow labyrinth with a siphon effect intended to empty the siphon through suction as the flexible bottle returns to its original shape. The very complex outflow path with a multitude of direction changes and a plurality of constrictions with thixotropic fluids causes the interior friction to produce a high resistance that must be overcome upon actuation and results in an abrupt outflow of fluid upon actuation. At the same time, such a labyrinth is also inevitably accompanied by a certain amount of residues that remain behind and dry out due to the inclusion of air inside the labyrinth path. These residues constrict the flow path, thus further exacerbating the above-described problems. It is known that closures of this kind become completely clogged over time and as a result, such closures are no longer on the market today.
U.S. Pat. No. 4,460,101 discloses such a labyrinth closure, with a support surface mounted underneath the spout. This closure has the above-described problems where the flow path is even more complex, resulting in this closure having an even greater tendency to become clogged. In particular, the latter patent mentions the use of thixotropic fluids. With the many direction changes and constrictions, the viscosity of the fluid is necessarily improved by the internal friction, but as mentioned above, the flow path is so complex that the function is only assured to a tolerable degree if the container is shaken vigorously beforehand, thus reducing the thixotropy and already changing the viscosity. Thus for practical purposes, the additional direction changes and constrictions are hardly needed anymore. Through corresponding testing, the applicant has simplified the closure according to this invention on the basis of the known prior art so that the problems mentioned no longer occur. With only one constriction and only two direction changes, it is possible to sufficiently reduce the thixotropy while at the same time, reducing the exerted force and leaving hardly any possibility for the closure to become sticky or clogged over long-term use. Despite the problem that has existed for years with closures of this kind, up until now, the market has not seen the introduction of any closures that are especially suited for thixotropic fluids and that do not become clogged, even with longer term use.